From the manufacturer

Men's UA Iso-Chill ArmourVent Adjustable Hat

This hat was designed to keep your head cool by dumping excess heat through special vents that allow hot air out, but are small enough that the sun's rays aren't an issue.

• ArmourVent Technology delivers ultimate breathability in a light, stretchy, durable & fast-drying fabric
• Material wicks sweat & dries really fast
• Iso-Chill sweatband & front panel lining helps disperse body heat, making it feel cool to the touch
• Adjustable back closure